1. Field of the Invention
This invention relates generally to completion of wells for the production of fluid therefrom and more particularly concerns a method and apparatus for accomplishing pressure testing of packers seals and other pressure containing components of a well during completion activities. More particularly, the present invention concerns the method for installing a production system within a well and, prior to initiating production operations, increasing casing pressure to a level for differential pressure closure of one or more differential valves of the production tubing string, further increasing casing pressure to test the integrity of all pressure containing components such as seals, packers, etc. After the pressure testing procedure has been completed, a fluid transfer valve is opened to permit transfer of well fluid from the casing annulus into the production tubing for unloading the casing of standing well fluid in preparation for production of the well. To accommodate the problem of potential kicking of the well caused by sudden release of formation pressure into the well casing during backside pressure testing, the fluid transfer valve incorporates a unidirectional valve for blocking reverse flow of well fluid from the well bore into the production tubing.
2. Description of the Prior Art
When typical well production systems are installed within wells, after the production tubing string has been landed it is desirable to accomplish pressure testing from the casing side, or backside of the installation, so that the sealing integrity of seals, packers and other pressure containing components can be assured. Otherwise, if a condition of seal or packer leakage should exist, the abrasive condition of the well fluid can cause erosion of or other damage to well components which can require the well to be reworked to ensure efficient production of well fluid. Seal integrity is highly desirable to ensure against well blowout resulting from seal and packer leakage. Where a well is being completed for gas-lift production or is adapted for unloading by gas-lift valves, many types of gas-lift valves will prevent casing pressure testing of this nature because the valves will open and prevent desired test pressure from being reached and held so as to confirm the integrity of the seals and packers. In such case, the mandrels of the production tubing string are typically equipped with dummy valves to isolate the production tubing from casing pressure while the well casing pressure is increased to test pressure. The casing or backside pressure test is then conducted to the desired pressure and for the desired duration to ensure the sealing integrity of the sealing components of the system. After pressure testing has been completed, wireline equipment is then used to replace the dummy valves of the mandrels with pressure responsive valves or valves that are otherwise controlled. This of course is a time consuming and expensive procedure because of the significant rig time and labor requirements that are involved.
In cases where the well casing is perforated at the production zone prior to backside pressure testing, the presence of elevated fluid pressure within the casing, which is necessary for backside pressure testing, can cause casing fluid to be forced into the producing formation surrounding the well casing. When this occurs, the formation can be damaged to the point that production from the well can be severely diminished. If, as in many cases, the well fluid is drilling fluid having a liquid carrier and containing fine, dense particulate such as barite and perhaps also containing contaminant particulate such as pipe scale, drill cuttings, metal fragments from the firing of perforating charges, etc., this liquid, slurry-like material can be forced into the formation and can block its fluid flow interstices. At times a formation seal can be developed by this material which interferes with flow of formation fluid, oil, water, natural gas, into the well bore. To prevent damage to the formation by backside pressure testing procedures it is desirable to conduct pressure testing activities prior to perforation of the well casing.
One of the principal problems with this type of pressure testing procedure is the possibility that the well can begin to kick, i.e., receive pressure from the earth formation in communication with the wellbore, at a point in the procedure where a dummy valve has been removed, but has not yet been replaced with a gas-lift regulating valve. In this case it could become necessary to kill the well by injecting fluid at a pressure exceeding formation pressure. This procedure can seriously damage the well and interfere with its subsequent production. Obviously, there is a significant risk of well blowout if the well begins to kick at a time when a valve is missing from one of the mandrel valve pockets. Also, since wireline equipment is required for retrieving dummy valves from the mandrels and replacing them with gas-lift valves, the expense of the wireline equipment and the wireline specialist personnel that are needed for wireline service activities adds significantly to the cost of the well completion procedure.
Another disadvantage of well completion activities that require wire line equipment for valve replacement is the cost of rig downtime. This is especially disadvantageous in the marine environment where rig costs and well servicing costs are prohibitive. It is desirable therefore to complete wells for production in such manner that eliminates the need for dummy valve installation and replacement and ensures, after backside pressure testing has been completed, that the well is immediately ready to begin production activities.